1. Statement of the Technical Field
The inventive arrangements relate to radomes, and more particularly to environmental protection systems for radome.
2. Description of the Related Art
Radomes are designed to protect enclosed electromagnetic devices, such as antennas, from environmental conditions such as wind, lightning, solar loading, ice, and snow. Conventional radome types include sandwich, space frame, solid laminate, and air supported. Radome induced wave perturbations are a principal consideration in radome construction. An ideal broad band radome is electromagnetically transparent to a large or selected number of radio frequencies, through a wide range of incident angles. However, in practice, conventional radomes are inherently lossy and are narrowbanded.
The walls of conventional radomes are formed from dielectric materials. Conventional teachings suggest that metals are generally to be avoided in radomes unless required by overriding environmental, electrical or structural considerations. For example, excessive ice buildup on a radome can cause poor performance and, in extreme cases, structural failure. Ice buildup can be prevented by the presence of heating wires disposed within the radome for preventing ice buildup. U.S. Pat. Nos. 4,999,639 and 5,528,249 each disclose the use of such heating wires in radomes. Similarly, metal wires incorporated in radome systems can be used as part of an effective lighting protection system. Finally, embedded metal wires can also be used as part of a grounding system to reduce static buildup on the dielectric surfaces of the radome.
Still, there are problems that arise from embedding wires within a radome. For example, current RF performance of radomes equipped with de-icing wires tends to be relatively poor. This poor performance also extends to radomes that use embedded wires for lightning and anti-static protection. The embedded wires act as polarizers and otherwise interfere with RF transmissions passing through the radome. In order to avoid such undesirable effects, it has been suggested in U.S. Pat. No. 5,528,249 that radome wires can be shielded from RF energy by strategically positioning the heating wires in selected areas of a frequency selective surface (FSS). However, the wires tend to degrade FSS electrical performance. These kinds of systems also require tight manufacturing tolerances since heating wires must not cross through certain portions of the FSS elements. Further, this arrangement is impractical for FSS designs that use triangular lattices since the wires, which are generally aligned in straight lines, will necessarily have to follow zigzag paths in order to avoid crossing over undesirable areas of the FSS elements, thereby degrading their performance. Finally, it will be appreciated that FSS scan angle stabilization cannot be effectively achieved with this approach since it requires adding a relatively thick dielectric layer between the heating wire surface and the exterior environment. This limitation is due to the proximity of the FSS surface to the heating wire surface.
Despite their drawbacks, embedded wire systems continue to be used in radomes for de-icing, lightning protection, and anti-static protection because such protection systems are essential in a variety of applications. Accordingly, there is a need for an improved protection system for radomes.